Ceramic materials such as silicon nitride, silicon carbide and the like have been said to be prospective materials as structural parts because they have excellent heat resistance and heat shock resistance. They have begun to be used, for example, as diesel engine parts in reality. However, it is preferred in respect of manufacturing technology and of manufacturing cost to use a ceramic material for a part requiring heat resistance and use a metallic material for a part requiring no heat resistance in such parts.
For that purpose, a method for joining a ceramic material to a metallic material becomes necessary. As the joining method, brazing through a metallizing method or the like, welding such as fusion welding and solid phase welding, a joining method with an inorganic adhesive or the like, shrinkage fit, and the like are known. Of these, the shrinkage fit method is the simplest method. With plate parts, a method for fastening them with bolts and nuts is also carried out.
However, when a ceramic material is subjected to shrinkage fit or is fastened with bolts and nuts, a compressive stress is formed in a surface of ceramic material in which the ceramic material is pressed by a metallic material and a tensile stress is formed in a free surface adjacent to the above-mentioned surface, in which the stress distribution condition shows a rapid change from compression to tension. Therefore, the ceramic material has a mechanically weak region and it breaks easily in the above-mentioned surface region under the above-mentioned condition.
The applicant filed the application (U.S. Application No. 694,759) for the invention of a method for sticking a metallic film firm to a ceramic material and at the same time, for improving the toughness of the ceramic material by forming a metallic film on the surface of ceramic material and irradiating it with high energy ions from above it.
The inventors had an idea that, if the above-mentioned invention was applied to joining of a ceramic material to a metallic material, it would be possible to reduce tensile stresses formed on the surface of ceramic material and to prevent the breakage of ceramic material in its joining area.